Production of crinkled cellulose ester filaments



Patented Nov. 2%, ice? PRODUCTION 01F GREH'KLED CELLULOSE ESTERFHLAMENTS William Evan Taylor, Spondon, near Derby, England, assignor toBritish Celanese Limited, London W. 1, England, a company of GreatBritain No Drawing.

Application February 18, 1944,

Serial No. 522,968. in Great Britain March 24,

5 Qlaims.

This invention is concerned with improvements in the production ofcrinkled cellulose ester filaments and particularly in the production ofartificial wool having a basis of cellulose acetate or other organicderivative of cellulose.

Wool is greatly valued as a textile fibre by reason of theheat-retaining qualities and soft handie of fabrics made thereof. Thesequalities appear to be associated in no small measure with the crlnklynature of the wool fibres. This has led to the production of crinklartificial fibres and these artificial wools" do exhibit in considerablemeasure the foregoing desirable qualities of wool. It is very desirablethat such artificial wools should have crinkle and soft handle in a highdegree and it is equally important that these qualities should not beadversely afiected when fabrics, garments and other articles made fromthe artificial wools are subjected to normal wear or laundering. It isfurther desirable that such articles should revert to their originaldimensions and shapes after distortion. Again, such artificial woolsshould be capable of being dyed evenly, as otherwise their value formany purposes is greatly diminished.

It has now been found that an artificial wool which exhibits in veryhigh degree indeed the above-mentioned properties desirable in anartificial wool can be obtained by subjecting to the action of hotaqueous media filaments which have been made by a particular method froma solution of an organic derivative of cellulose, particularly ofcellulose acetate.

According to the present invention, artificial filaments capable ofyielding an improved artificial wool are obtained by extruding a.solution of an organic derivative of cellulose in a volatile solventthrough a spinning jet into a cell through which a current ofevaporative medium is passed. said solution having a, viscosity notexceeding 50 when determined as described below and, as it enters thespinning jet, being at a temperature below the boiling point of thesolvent at atmospheric pressure.

The viscosity of the spinning solution or "dope is measured bydetermining the time in second for a steel ball weighing 0.7 gm. andhaving a, diameter of 1" to fall through 3" of the solution at 25 C. Thenumber of seconds is taken as representing the viscosity. Preferably asolution having a viscosity of from 25 to 30 is used in the productionof artificial filaments by the process of the present invention.

The viscosity of the solution is dependent on the concentration ofcellulose derivative in the solution. It is also dependent on theviscosity of 2 the cellulose derivative which is usually measured bydetermining the rate of flow of a fairly dilute solution of thederivative through anOstwald viscometer. For instance, viscosities ofthe acetone-soluble cellulose acetates mentioned in this specificationwere determined by comparing the rate of flow of a. 6% solution of theacetate in acetone at C. with that of glycerine taken as 100. Thus asolution which has a rate of flow such that the level of thesolutiondrops from the upper marl; to the lower in 20 seconds, whereasglycerine requires 100 seconds under the same conditions, contains anacetate having a viscosity of 20.

The process of the present invention is of particular value in theproduction of filaments capable of yielding artificial wool fromsolutions oi. lower fatty acid esters of cellulose, e. g., celluloseacetate, cellulose propionate, cellulose butyrate, celluloseacetate-propionate and cellulose acetatebutyrate and in the productionof artificial wool from these filaments. Of the lower fatty acid esters,cellulose acetate is the most important and the invention will thereforebe particularly described in relation to the production of artificialfilaments having a basis of this ester and of artificial wool therefrom.

The normal method of producing cellulose acetate filaments consists inspinning a solution of cellulose acetate in acetone, containing about25% by weight of cellulose acetate, at a tempera ture of 70-80 C. into acounter-current of air which is at a similar temperature. The productionof cellulose acetate filaments by the process of the present inventioninvolves the spinning of a solution of cellulose acetate at a lowtemperature into an evaporatlve medium which is preferably also at a lowtemperature, employing a spinning solution or dope which has a lowviscosity. Filaments may thus be obtained which crinkle extremelyreadily, evenly, and to an exceptionally high degree under the influenceof hot aqueous media, compared with filaments obtained from the samecellulose acetate under ordinary conditions. If, however, one or more ofthe foregoing spinning conditions are not observed, the result ingfilaments yield less satisfactory artificial wool upon subjection to hotaqueous treatments.

As an indication of spinning conditions which have been found suitable,it may be stated that, when using a solution in acetone of ordinaryacetone-soluble cellulose acetate having a viscosity of between 10 and20, a dope temperature between 40-45 C., an air temperature in the callfrom about -40 C. down to the dew point, and

a cellulose acetate concentration of about 1822% are usually suitable.It will be noted that the temperatures employed are below the boilingpoint of the solvent present in the dope and that the low concentrationof cellulose acetate will result in a dope of low viscosity. The lowerthe temperature, particularly of the dope, and the lower the celluloseacetate concentration, the more readily in general are the filamentscrinkled by hot aqueous media and the better is the artificial woolproduced. The temperatures and concentration cannot, however, be reducedbelow a certain minimum, which varies with the viscosity of thecellulose acetate and the other spinning conditions, if stable spinningis to be obtained. Usually, temperatures should be of the order of thosegiven above. However, if it is desired to reduce the time required forthe setting oi. the filaments the air temperature may be increased up toabout the boiling point of the dope solvent, e. g.,'55-60 C. whenacetone is used. If an acetate or high viscosity, for'example 50, 80,100, 200 or more, is used, then there is a corresponding decrease in theminimum dope concentration which can be employed without reducing thedope viscosity below that necessary for stable spinning.

The use of low temperatures and low dope concentrations increases thelength of time required to efiect setting of the extruded filaments andit is, therefore, in general necessary either to spin at a slower speedthan that usually employed in the dry-spinning of cellulose acetatefilaments or to increase the length of the path of the materials throughthe evaporative medium. Both these expedients may, of course, be adoptedin order to efiect setting of the materials. For example, spinningspeeds of 100 to 150 or 200 metres per minute may be employed, insteadof the speeds of 300 or 500 metres per minute or even more used in thecommercial production of ordinary cellulose acetate filaments, and thepath of the materials through the evaporative medium may be increased to15, 25 or 30 feet, or more Provided that the filaments pass for asubstantial distance, e. g.. 10, 12 or 15 feet, through an evaporativemedium at a relatively low temperature, so that the major proportion ofthe solvent has been evaporated and the cross-sectional form of thefilaments is established, they may then pass through a hotterevaporative medium, at a temperature of. e. g., Gil-80 C.. in order toaccelerate removal of any residual solvent. In such cases it isconvenient to use a co-current of evaporative medium so as to preventoverheating of the evaporative medium into which the filaments firstpass.

As indicated above, the most important factors in the production of thefilaments according to the present invention are the use of a low dopeconcentration and of a low dope temperature. A further factor which isof importance is the concentration of solvent in th evaporative medium,particularly in the region of the jet. In general, it is found that itis desirable to have a higher concentration of solvent in this regionthan is the practice in the production of ordinary cellulose acetateyarns. For example, using a countercurrent of air the volume ratio ofair to dope may be adjusted so that the outgoing air contains 2% ofacetone by volume instead of about 14.5%, which is a normal figure, thusincreasing the acetone concentration in the region of the Jet.

In order to produce the artificial wool the filaments, either incontinuous form or after conversion into staple fibre, are subjected totreat-- ment with a hot aqueous medium. Preferably they are heated forabout 2-4 hours in a solution of a wetting agent, e. g., a soap solutioncontaining, for instance. 0.5 to 1% of soap at a temperature from -1000., though wet steam or hot water alone may be employed. The treatmentshould be carried out so that the filaments are free to contract andcrinkle.

Continuous filaments are preferably assembled into yarns, with orwithout twisting, at the time of spinning and the yarns are subjected tothe hot aqueous treatment in hank form. When the filaments have beencrinkled the yarns may be twisted or further twisted and if a heavierdenier yarn is required a number of ends may be assembled and thentwisted either with the same twist or with a reverse twist to thatemployed with the single ends. Usually it is preferable to use a reversetwist. The method of twisting and whether one or a number of ends areemployed will, however, depend upon the nature of the yarns which it isdesired to produce. For instance, if artificial wool yarn of heavydenier is required it is generally desirable to form it from a number ofends whereas a yarn of light denier may consist of only one end.

Yarns may also be obtained according to the present invention bysubjecting the assemblies of continuous filaments after spinning to aprocess of twisting, setting the twist and removing the twist such as isdescribed in U. S. Patents S. Nos. 2,089,198, 2,089,199 and2,1l1,211--preferably prior to treatment with a hot aqueous medium.Filaments in the form .of staple fibres may be spun into yarns eitherprior to or after crinlsling by a hot aqueous treatment. Again, yarnsmay be employed in the pile 01 a pile fabric and the pile then crinkledby a hot aqueous treatment.

The following example is given to illustrate the production of wool-likeyarns by the process of the present invention.

Example A 21.5% solution of a cellulose acetate, having a viscosity ofabout 16, in a liquid medium consisting of acetone and 5% water was spunthrough twin jets into a cell and taken up at about metres per minute.The viscosity of the spinning solution, determined as described above,was 25 and its temperature at the exit from the candle, i. e. onentering the jets, was 42. The spinning conditions were such that eachend had a total denier of about 340. The extruded filaments were passedfor about 15 feet through a current of air at a temperature of 30-35 C.and the two ends were then taken up together outside the cell on capspinning bobbins which inserted an S twist of 0.4 turns per inch intothe yarn. The yarn was then hanked and the hanks heated for about 4hours at a temperature of 90-100 C. in a 0.5% soap solution, after whichthey were washed and dried. The twist in the yarn was then increased toabout 3 turns per inch after which three ends were doubled together witha Z-twist of 3 turns per inch. A yarn was thus obtained which dyedevenly and after finishing was very suitable for a hand-knitting yarn.

As has already been stated, yarns may be obtained by the process of thepresent invention which have outstanding properties as artificial wooland indeed in some respects are better than wool itself. For example,the permanent, stretch of a sample of all-wool hand knitting yarn, afterstretching in dry and wet states under certa conditions, wasrespectively 26% and 29.5%,

; while that of the cellulose acetate yarn obtained '5 as describedabove was only 4.8% and 16.0% respectively under the same conditions. Itwas also stronger than the wool sample when wet. As a consequence of theabove improved properties articles can be made from the yarns which aremuch more resistant to stretching than articles made of pure wool andwhich thus keep their shape much better. For example, jumpers knittedfrom artificial wool obtained as described above retained their shapeand showed negligible shrinkage after they had been washed ten times.

While, as indicated above, yarns produced by the spinning processdescribed in the present application are particularly valuable forconversion into artificial wool by treatment with hot aqueous liquidsthey are also of value for other purposes. They may, for example, beemployed without further treatment for the production of fabrics andother articles. Special efiects may be produced by treating articlescontaining such yarns, either alone or combined with other yarns, withhot aqueous media so as to crinkle them.

The process of the present invention has been described particularlywith reference to the proa lose acetate in, acetone through a spinningjet into a cell through which a current of air at a temperature at leastC. below the boiling point of acetone is passed, said solution having avisduction of filaments and artificial wool from cellulose acetate but,as has already been stated, it is also applicable to the production offilaments and artificial wool from other organic derivatives ofcellulose. As indicated above the lower the dope concentration and thelower the temperatures of the dope and the evaporative medium, thebetter in general are the filaments produced for conversion intoartificial wool, provided that stable spinning can be obtained. Thetemperatures employed will depend largely upon the nature of the solventmedium used and in general it is desirable that they should besubstantially below its boiling point at atmospheric pressure, e. g., atleast 10 C. lower. The dope concentrations which are suitable willdepend on the cellulose derivative and solvent employed, but they willin any case be such as to yield a solution 1 having a viscosity below 50and will be low enough to yield one of 25-30. I

Having described my invention, what I desire to secure by Letters Patentis:

1. Process for the production of textile materials, which comprisesforming continuous artificial filaments by extruding a solution of alower fatty acid ester of cellulose in acetone through a spinning jetinto a cell through which a current of air at a temperature at least 100.. below the boiling point of acetone is passed, said solution having aviscosity between 25 and 50 :when determined as hereinbefore describedand,as it enters the spinning jet, being at a temperature below theboiling point of the solvent .at atmospheric pressure.

2. Process for the production of textile materials, which comprisesforming continuous artificial filaments by extruding a solution ofcellupreferably cosity between 25 and 50 when determined as hereinbeforedescribed and, as it enters the spinning jet, being at a temperaturebetween and C.

3. Process for the production of textile materials, which comprisesforming continuous artiiicial filaments by extruding a solution ofacetone-soluble cellulose acetate in acetone through a spinning jet intoa cell through which 5, current of air at a temperature at least 10 0.below the boiling point of acetone is passed, said solution having aviscosity between 25 and when determined as hereinbefore described and,as it enters the spinning jet, being at a temperature below the boilingpoint of the solvent at atmospheric pressure, and the rate of flow ofair through the cell being such that on issuing from the cell itcontains at least 2% of acetone by volume.

4. Process for the production of textile materials, which comprisesforming continuous artificial filaments by extruding a solution ofcellulose acetate in acetone through a spinning 'jet into a cell throughwhich a current of evaporative medium at a temperature at least 10 C.below the boiling point of acetone is passed, said solution having aviscosity between 25-and 30when determined as hereinbefore described,and, as it enters the spinning jet, being at a temperature between40and450. I

. 5. Process forthe production of artificial wool, which comprisesforming continuous artificial filaments by extruding a solution ofcellulose acetate in acetone through a spinning jet into a cell throughwhich a current of evaporative medium at a temperature at least.10 C.below the' boiling point of acetone is passed, said olution having aviscosity between25 and 50 when determined as hereinbefore describedand,jas'it enters the spinning jet, being at a temperature between 40and pheric pressure until crinkling is efiected.

WILLIAM IVAN TAYLOR.

' REFERENCES crrEn The following references are of record in the flleofthis patent I g UNITED STATES PATENTS 2,232,012 Rooney etal. Feb. 18,1941

